Re: [PHP-DEV] [RFC] Primary Constructors

Hi

Am 2026-06-29 22:22, schrieb Rob Landers:
> This was an oversight. I'll add the logic there. This is how they work:
>  1. Attributes on promoted primary-constructor params are reflected on 
> both (just like promoted properties):
>    1. ReflectionParameter
>    2. ReflectionProperty
>  2. Attributes on bare params remain parameter-only.
>  3. Target validation is context-sensitive, matching existing 
> constructor promotion behavior:
>    1. `#[ParamAttr] public int $x` appears on the property too, but 
> newInstance() from ReflectionProperty errors.
>    2. `#[PropAttr] public int $x` appears on the parameter too, but 
> newInstance() from ReflectionParameter errors.
>  4. Attributes before a class remain class attributes and are not 
> copied to the synthesized constructor.
> The last one is debatable, but from what I can tell from grepping, 
> putting attributes on constructors is a very rare thing (39 out of 
> 56,546 constructors). However, class-level attributes are a more common 
> thing. That being said, I'd be open to changing (4) to behave like 
> properties/parameters where it gets attached to the class and the 
> constructor.

Thank you for confirming my assumption that expectations likely differ 
(https://news-web.php.net/php.internals/131610).

I would expect #[Attr] to be applied to both `Foo` and 
`Foo::__construct()` for consistency with promoted properties, since 
“Primary constructors” are effectively “Promoted Constructors”:

     #[Attr]
     class Foo(public int $x) { }

The error on the `newInstance()` will only be an issue for code that 
tries to unconditionally instantiate unknown attributes, which is bound 
to fail already since attributes do not need to be backed by a class - 
and arguably doing so is not super useful, since you don't know the 
semantics of unknown attributes. Code that knows what a given attribute 
means will not try to find it on mismatching targets and thus will not 
try to instantiate them either.

Best regards
Tim Düsterhus